JPH05154661A - Upset welding method - Google Patents

Abstract

PURPOSE:To form a sound weld zone free from defective cold pressure welding with the short upset length by setting the pressurizing force in the preheating stage at two stages and setting the pressurizing force at the second stage lower than that at the first stage. CONSTITUTION:The pressurizing force P1 is impressed and energizing is started. The pressurizing force is then reduced and made to P2. At a point of time when a butt part attains the sufficiently high temperature, the preheating stage is forcibly changed over to the upset stage. The changeover from the preheating stage to the upset stage is carried out by setting a timer. Consequently, a sound welded joint is easily realized with the short upset length.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a butt resistance welding method, and relates to an upset welding method suitable for welding steel plates, steel bars, pipes and the like.

[0002]

2. Description of the Related Art Among butt resistance welding, upset welding is widely used in place of flash welding because it is suitable for automation because it does not cause flash during welding and does not stain, unlike flash welding. There is.
In the upset welding process, first, objects to be welded to each other are clamped on a fixed base and a movable base, respectively, and end faces to be welded are abutted against each other to apply a constant pressing force. After that, a preheating process is started in which a welding current is applied to heat and soften the object to be welded by using Joule heat generation due to the specific resistance of the object to be welded and the contact resistance of the butted portion. As the temperature rise softens, the butt joint deformation starts at a temperature corresponding to the applied pressure, the moving table advances toward the fixed table, and the upset process starts, causing a large plastic deformation in the butt section. Welding is completed.

The advance distance of the movable table at this time is called an upset length. Generally, if the upset length is increased, the quality of the welded portion is improved accordingly. However, in order to improve the material yield, it is necessary to make the upset length as short as possible and perform welding efficiently. For that purpose, the plastic deformation may be concentrated near the abutting portion. In order to concentrate the plastic deformation in the vicinity of the abutting portion, it is sufficient to concentrate the heat input in the vicinity of the abutting portion. Therefore, the pressure applied in the preheating step may be reduced to increase the contact resistance or increase the current density.
However, if the applied pressure is made too low or the current density is made too high, localized heat generation will occur, causing the heat to shift to the upset process with a non-uniform heating state, or the local heat generation part may melt and explode before the upset process. There is. Therefore, in the determination of the welding conditions, it was usual that the applied pressure in the preheating step is as low as possible and the current is as high as possible so that local heat generation does not become significant.

In this way, the inventions of JP-A-61-38787 and JP-A-61-38788 have been made from the viewpoint of welding machine control as a method for successfully suppressing local heat generation. In particular, Japanese Patent Laid-Open No. 61-38788 discloses an upset welding method characterized in that a welding current is intermittently applied and the pressing force is reduced during the welding current application period in synchronization with the welding current application cycle. is suggesting.

[0005]

However, it is generally difficult to control the pressing force in a short time by synchronizing the welding pressure with the welding current as in the above-mentioned conventional upset welding method, and the pressurizing mechanism becomes complicated, and the equipment adjustment is performed. Becomes subtle. Moreover, since the welding current is stopped intermittently, the welding time becomes longer than in the case of continuous energization, heat input cannot be concentrated near the butt portion, and plastic deformation cannot be efficiently concentrated near the butt portion. Furthermore, the contact area between the objects to be welded increases due to the high pressing force while the welding current is stopped, and the current density per unit area decreases in the next energization period, so the weld temperature cannot be increased and the When the strength is increased, there is a problem such as frequent welding defects called cold welding due to insufficient heat input.

The present invention has been made in view of the above problems, and suppresses local heat generation when performing upset welding to complete welding of an iron-based member through a preheating step and an upsetting step, and at the same time, upset The object of the present invention is to form a sound weld without a cold welding defect with a short upset length by increasing the temperature of the immediately preceding butt portion as much as possible. In addition, a method for easily performing upset welding is also proposed by proposing a timing determination method for switching from the preheating step to the upset step.

[0007]

In order to solve the above-mentioned problems, the present invention provides an upset welding method for completing welding of an iron-based member through a preheating step and an upset step,
The present invention proposes an upset welding method characterized in that the pressing force in the preheating step is set to two steps and the pressing force in the second step is set lower than the pressing force in the first step.

Further, as the timing of switching from the preheating step to the upset step, the voltage drop amount between the objects to be welded is measured and the time when this voltage reaches a preset reference voltage is set, or the second stage pressing force is being applied. The present invention proposes an upset welding method, which is characterized in that it takes a time when an electrode movement amount reaches a preset reference amount.

[0009]

According to such an upset welding method, it is possible to make the current distribution uniform and suppress local heat generation by accommodating the abutting surfaces while the first step pressure is being applied in the preheating step. Next, by setting the second-step applied pressure lower than the first-step applied pressure, it is possible to reduce the deformation of the work piece, maintain the contact resistance of the butted portion at a high value, and efficiently perform Joule heat generation. Therefore, the temperature of the butted portion can be increased.

Further, the amount of voltage drop between the objects to be welded is measured,
At the time when this voltage reaches a preset reference voltage, or when the amount of electrode movement during application of the second-stage pressure reaches a preset reference amount, it is possible to switch from the preheating process to the upset process. For example, it is not necessary to set a timer for the second-stage pressing force application time, and it is possible to keep the temperature of the butted part just before the upset constant, despite the difference in the heat generation state of each work piece due to the difference in the butted surface state. As a result, it is possible to easily form a sound weld without a cold welding defect with a short upset length.

The pressure applied in the upsetting process is set higher than the second pressure applied in the preheating process, and the preheating process is forcibly switched to the upsetting process. This is because if the current is maintained at the same value as the second-stage pressure in the preheating process until the upset process starts, the amount of heat generated is too large and the butt portion melts and explodes.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An upset welding embodiment of the present invention will be described below with reference to the drawings. Plate thickness as test material 2.
8mm, Ti addition of 150mm width corresponding to welding line length 8
0 kg class hot rolled steel sheet is used.

Welding starts by applying a pressing force P ₁ shown in the figure between the abutting surfaces of the objects to be welded. In the case of this embodiment, P ₁ is 12.5 Kgf / mm ² . In this state, energization is started, but I _{1 in the} figure is 140 Amp / mm ^{2 in} the case of this embodiment.
Then, this current value is reached in 10 cycles of upslope,
In the figure, the energization time of T ₁ was set to 2 cycles. Here, one cycle is 0.02 sec.

Next, according to the present invention, the applied pressure is reduced to raise the temperature of the butted portion. In this example, 8 Kgf / mm ² was selected as P ₂ in the figure. For the current value during application of the pressing force P ₂ , I _{2 in} the figure, 140 Amp / mm ² which is the same as I ₁ was selected in this embodiment. The energization time, T ₂ in the figure, was 8 cycles. The abutting portion is heated to a higher temperature more efficiently and higher than the case where P ₂ is not lowered below P ₁ during this energization period. As the temperature rises at the abutting portion, the electric resistance of the members increases, and the inter-electrode voltage reaches a higher value than in the case where P ₂ is not lowered below P ₁ .

It is necessary to forcibly switch to the upset process when the temperature of the butted portion reaches a sufficiently high temperature. If this is not done, the temperature of the abutting portion will rise too high, causing melting and explosion. In this example, the preheating process was switched to the upset process by setting a timer. At this time, the pressing force at upset, P ₃ in the figure is 12.5 Kgf / mm ²
And In addition, the energization continues during the upset process,
In the figure, 140 Amp / mm ² was selected as I ₃ , an energization time, and 4 cycles were selected as T _{3 in} the figure. The down slope is 3 cycles. The upset length in this embodiment is 5 mm.

In order to confirm the quality of the welded portion, a bending test was performed after grinding the upset deformed portion. When the quality of the welded portion is shown as a percentage of the length of the defective opening portion with respect to the length of the weld line, the average opening portion ratio in this example was 0.1%. On the other hand, all the pressures P ₁ , P ₂ , P _{3 in the} figure are set to 1
At 2.5 Kgf / mm ² , large cracks were generated in 6 out of 10 test pieces due to cold welding defects, and the average opening ratio was 55%. In addition, when the pre-heating pressure is set low from the beginning of welding, that is, P ₁ and P _{2 in the} figure
Is 8 Kgf / mm ² and pressing force P ₃ at upset is 12.5 Kgf / mm ² .
When it was set to mm ² , the local heat generation was intense and the welding was not stable.

In this embodiment, the timer is used to switch from the preheating process to the upset process. However, after the voltage between the electrodes reaches a certain value, the switching is performed or after confirming that the displacement of the movable table exceeds a certain amount. You can also switch.

[0018]

According to the present invention described above, cold welding defects in upset welding can be eliminated with a shorter upset length than in the prior art, and even in high tensile steel of 60 Kgf / mm ² grade steel or more, it is easy. It is possible to realize a sound welded joint, and its industrial value is very high.

[Brief description of drawings]

FIG. 1 is a time chart showing a pressing force, a current, a displacement of a moving table, and a voltage between electrodes in main welding.

Claims (3)

[Claims] 1. An upset welding method for completing welding of an iron-based member through a preheating step and an upsetting step, wherein the pressing force setting in the preheating step is set to 2 steps, and the pressing force in the 2nd step is set to a value higher than that in the 1st step Upset welding method characterized by setting low. 2. The upset welding method according to claim 1, wherein the inter-electrode voltage is measured, and when the voltage reaches a preset reference voltage, switching to the upset process is performed. 3. The upset welding method according to claim 1, wherein the upset step is switched to the upset process when the electrode movement amount during application of the second step pressure reaches a preset reference amount.